Synthetic polyester yarns have been known and used commercially for several decades, having been first suggested by W. H. Carothers, U.S. Pat. No. 2,071,251, and then by Whinfield and Dickson, U.S. Pat. No. 2,465,319. In particular, polyester staple fiber has been an industrial commodity that has been manufactured and used in such textile yarns on a very large scale, primarily in blends with natural fibers, especially cotton, such blends having been spun (twisted) into spun yarns that have been made into textile fabrics, and eventually into garments and other textiles. Practically all such polyester staple fiber has been of round cross-section and solid, as opposed to hollow; references herein to solid refer to such solid cross-section. Such staple fiber is generally of average denier about 11/2 and of cut length about 11/2 inches, but the average denier and cut length can vary up to about 3 and down to about 1, and the ratio of average denier to cut length is generally about 1 and less than 2:1. Polyester staple fiber has been recognized as having significant advantages over cotton in some respects, for instance its thermoplastic characteristics that enable polyester-containing fabrics to hold their shape, for instance a crease, and to have wash-wear characteristics, their greater uniformity, which provides processing advantages and their superior strength and resistance to degradation. However, hitherto, some people have expressed a preference for wearing garments from cotton fibers because of attributes that can be summarized as "comfort", to the extent that there has been a trend recently towards reducing the content of polyester in blends, and even to using more 100% cotton fabrics, despite the practical advantages of wash-wear 100% polyester and blended fabrics. Because of the sophistication of the textile industry, both of the polyester fiber manufacturing industry and of downstream consumers of textiles, and because of the commercial interest in providing apparel and fabrics that will perform well during actual use by the ultimate consumer (wearer), much attention has been devoted to analyzing appropriate requirements. Many technical papers, for example, have been published on various aspects, and patents have been issued with the objective of improving the "comfort" that can be obtained from textile articles, and their constituents, and the literature has been replete with these suggestions for several years. So it has long been considered desirable to improve various properties of polyester-containing textiles, and of the yarns and polyester staple fibers, themselves, and much effort has been devoted in the textile industry towards this objective.
An important objective of my invention is to provide such polyester staple fiber, or its precursor tow, in a new form such that it can be formed into spun yarns, which can then be formed into fabrics and garments that can show improved moisture-wicking properties, as discussed hereinafter.
Polyester filaments are characterized by their extreme hydrophobic character, as mentioned in "Polyester Fibres--Chemistry and Technology", by H. Ludewig--English translation 1971--John Wiley and Sons, Ltd., in Section 11.1.5 on pages 377-378, and also in Section 11.4 on dyeing properties, starting on page 398. Indeed, the difficulty of dyeing polyester yarns and fabrics is notorious. Ludewig's book mentions many aspects of polyester fibers and their preparation and properties.
Polyester staple fiber has generally been manufactured commercially by a process of melt-spinning (i.e. extruding molten polyester polymer) into a bundle of filaments, collecting such filaments into a tow, which can be relatively small and converted directly, e.g. by stretch-breaking, into a spun yarn, but has more often been extremely large, amounting to many thousand and even some million(s) of filaments, and this tow has then been processed by drawing, and possibly annealing, and crimping, before the crimped filaments have been converted into staple fiber by cutting, or otherwise, to the desired lengths. As indicated, most polyester staple fiber has then been blended, e.g. with cotton, and converted into yarn, which is generally referred to as a spun yarn, to distinguish it from a continuous filament yarn.
It is conventional to coat the freshly-extruded filaments with a "finish", which is generally an aqueous emulsion comprising a lubricant and an antistat. Finishes are discussed briefly in Section 5.5, starting on page 193 of Ludewig, referred to above As mentioned on page 195, the literature reveals relatively little about the compositions of the spin-finishes that are actually used. Although there is now considerable patent and other literature, the precise finish formulations are generally closely-guarded secrets by the yarn manufacturers, and different compositions are formulated for different purposes, depending on the particular intended processing and possible specific requests by individual customers, and these formulations change, sometimes quite frequently. As will be related hereinafter, a dramatic change in the surface properties of the fibers, and of articles containing them, such as yarns, fabrics and garments, has been obtained in effect by a relatively simple modification of the spin-finish that is applied to the freshly-extruded polyester filaments. Conventionally, the spin-finish is the first contact that a freshly-extruded filament encounters after solidification. The finish was generally applied by a finish roll, rotating in a bath of the finish, so that the filaments pass through the finish emulsion as they brush past the finish roll on their way from the solidification zone to the feed roll that determines the withdrawal speed from the spinneret. Before the finish roll, it is generally desirable to avoid or minimize contact between the filaments and solid objects, and so the only other closely-adjoining solid objects are generally guides that are intended to confine the filaments before contacting the finish roll. A finish roll is not the only method of applying finish, and other methods have been used and suggested, including spraying or metering the finish onto the filaments.